Double checking HT oven temp

[JTknives]

After building my oven my first question is to the temp accuracy. Wanted to know if I could trust what the display was showing me. So I ordered some temp sticks. I found a good deal on some on Amazon called thermomelt made by markal. I ordered them in 1400°, 1450°, 1480°, 1500° and 1550°. I also got some in the higher range. One reason I'm making this post is to pass out a warning to anyone else that is considering buying this brand. I tried the draw a line and heat but no work. These markers are very hard and don't draw a line. At first I was kinda pissed as I could not get anything to work. I was getting weird results. I then tried just touching the steel in the oven with the stick in the jaw of the tongs. The end of the stick would just crumble like wet sand. So then I tried putting little chunks onto a steel plate and just trying to melt them. No luck even after heating and trying to smear it with another bar of steel. The weird thing was the area around the chunk would look wet but the chunk was still there. Then the other day I got so fed up I called the company and talked to a guy that was sapost to everything. I explained what was happening and he was baffled. I explained the wet look and asked what do these do when that "melt" she said thy can be crumbly. I told him I tried to just melt a chunk in the oven on a bar of steel and it did not melt. He said it should have at least changed shape into a blob. I said nope nothing just a wet spot around it. I said it's like the binder is melting out of the stick and leaving the grains there. He said that's exactly what's happening. And said the grains should melt. He then blew my mind and said did you go hotter? Face palm, I said I went like 50° hotter but nothing. He said go hotter, these markets are guerenteed to +-15°. I said ok I will try that.

I then went to the shop and relazed I might have an issue that I never even considered. I swapped out my TC with a very fine thin wire TC. It measures the temp very fast and keep the oven from over shooting. I reliezed it was still in there. I swapped it out with my massive TC and fired up the oven. I let it equalize at 1480° for one hr. Then I slipped in my bar of steel with 4 chunks of temp stick on it. 1450°, 1480°, 1500° and 1550°.

I had tried this befor but never did anything. My thought was if it was high or low at least one of these would pick it up. I let it sit in the oven for 10° and opened the door and hot damn it worked.

Come to find out my thin Wire TC was way off by 100° or more. This error would not show up Until it got into the higher temps. But this TC plugged into a pid is what put me down this road any way because it would show my oven was much hotter then what the control would say. But it was wrong I guess, never trust cheep Chinese wire TC. But looking at my test the 1450° and 1480° melted perfect and the 1500° and 1550° was untouched. You can see a wet area under them but as was discovered that's just binder. So I'm real happy to know I'm at least within an close range of what the controller says.

So let that be a lesson learned. Just because you think something is wrong does not mean it is. But I would highly recommend if you have an oven to test it. Because of my oven was off by that much with that cheep TC so could yours if something is off. If any of you want to do the same test I would be more then happy to sent you some chunks of my stick so you could do this test.

 

[Bamph]

Very good to know! I need to do this too.

 

[Rick Marchand]

Tempilstiks don't really work like that, bud. I used them for many years in our fabrication shop. You have to swipe what you are checking. You can't just place them on a plate. They'll be affected by the IR radiation and may not tell you what the forge walls and contents truly are at. Maybe if you shield them in a small curl of stainless foil. A great way to check your oven is with the Curie point of iron. 1418F. Sneak up on the temperature with increments of 2-3F

 

[scott.livesey]

the Tempilstiks I bought would not mark, i was using a piece of CRS and they wouldn't leave a mark. they were dry and crumbled, so put some in a pile and into the furnace. had two thermocouples within an inch or so of the mark, when it melted, one probe was +5 the other -5 of Tempilstik temperature. I probably got some stock that had been on a shelf for years.
scott

 

[Stacy E. Apelt - Bladesmith]

I think I am responsible for some of the problems. I may have misstated the instructions. I have used the cones and the sticks. They work differently. Tempil sticks melt and make a mark when the steel is at the rated temperature. They barely make a mark on steel below the rated temperature. The instructions are right on the stick.

It has been a while since I used them to check anything, but they always worked for me to indicate/check a desired temperature. Where they really shine is for pre-heat in welding. You heat the object with a torch and stroke the crayon across the surface as it heats up until the crayon melts. Check several places to assure the whole object is at pre-heat. When the crayon says all is good, weld away.

To check an oven, you use three crayons rated about 20° apart - say 1430, 1450, 1470. You set the oven to 1450F and let the bar soak until the oven is stable ( 15 minutes at temp). Then you pull the bar and quickly strike each crayon. They only melt at the rated temp. If the 1430 melted and the 1450 and 1470 didn't, that indicates the temp is between 1430 and 1450. raise the temp 5° and let the steel soak for 5 minutes after the oven stabilizes at 1455F. Test again. If the 1430 and 1450 now melt, and the 1470 doesn't. , that indicates that the oven is within 5° of correct. The Tempil sticks have a range of +/- 15°, so you are pretty much in the right ball park. You can raise the temp to 1470F and 1475F and check that crayon for melting.

So, to repeat, a Tempil stick is drawn across the HOT metal and will melt in a liquid stripe if the temperature is at or above the rating of the stick.

If I stated it in the wrong way in the past, I apologize.






JT, as I suspected from your PM, the TC was bad. Sorry if my explanation of doing a Tempil stick test was misleading. The "while in the oven" statement was wrong ( I was thinking of the cones), and it would have been more clear if I had said "melts and doesn't"

My PM was -
"....What I would suggest is getting a set of three to five Tempil-sticks. They are reliable and will make the change while in the oven. You open the oven and pull the sheet of steel and see what melted and what didn't. Put it back and increase temp and check again in 15 minutes, etc. They can zero in the temp pretty accurately.
..."

 

[JTknives]

I talked to the guy about just melting chunks and he said that's fine. The material just melts at X temp so al long as your at that temp it will melt. As to the ir of the coils that's why I let the oven even out for an hr. The elaments cycle very little when fully soaked. To prove this I will do the same test but shielded tomarow.